Across the country, engineers, recyclers, researchers and entrepreneurs are finding new ways to give end-of-life tires a second life.
As part of USTMA’s Full Circle platform and America 250 Second Life Stories initiative, these stories highlight the people helping build sustainable end-use markets for recycled tires while solving real infrastructure challenges in their communities.
NOVA SCOTIA, CANADA
Dr. Hany El Naggar, Professor of Geotechnical Engineering, Dalhousie University
Every TDA project that gets built in the United States rests, in part, on a foundation of research. Engineering is not an industry that moves on enthusiasm. It moves on data, standards, and reproducible results. That’s what makes the work of Dr. Hany El Naggar at Dalhousie University so consequential for the U.S. tire recycling industry, even though his lab is based in Canada.
Pioneering the Research
Dr. El Naggar leads one of North America’s most active research programs on Tire Derived Aggregate. His team has published extensively on TDA’s behavior under static and dynamic loads, shear strength characterization of TDA and TDA soil mixtures, the compressibility of large aggregate sizes, and the seismic response of TDA-reinforced foundations, to name just a few topics. This is the kind of foundational science that moves from academic journals into ASTM standards and into design specifications that practicing engineers can rely on.
For USTMA’s 2025 State of Knowledge Report on TDA (the first report of its kind focused specifically on TDA market implications), Dr. El Naggar served as the lead author. It’s a document designed to do exactly what his research aims to do: translate what the science says into language that helps practitioners build with confidence.
“TDA is a product that is both lighter and stronger than traditional soil backfill. It diverts waste from landfills, turns it into a revenue stream, and has a wide range of applications. Once we demonstrate that, we’ll go from working to create demand to having to keep pace with it.” Dr. Hany El Naggar
From Soft Soils to Stronger Foundations
Nova Scotia, where Dalhousie is located, has soft marine clay soils in some areas, the kind of ground that can’t readily support infrastructure without significant engineering intervention. Dr. El Naggar’s research has shown that TDA-soil mixes used as backfill can reinforce foundation soil dramatically, enabling construction on sites that would otherwise require expensive pile foundations or be avoided entirely. The material is lightweight enough not to add problematic load, but strong enough to stabilize.
His team has also pioneered using TDA to reduce vibration and seismic demand on buried infrastructure, research that directly enabled transit projects deployed by Joaquin Wright and his team in California. When an ASCE paper and a CalRecyle field installation tell the same story, the confidence of the practicing engineer increases. That alignment between the lab and field is the product of researchers and practitioners who stay in close contact.
What the Data Shows
The USTMA State of Knowledge Report synthesizes what the research community has established about TDA’s effectiveness across application categories. On stormwater, studies show that TDA infiltration galleries reduce concentrations of heavy metals and pollutants, with no exceedance of primary drinking water standards. In road construction, TDA improves drainage, reduces frost-related damage, and mitigates differential heave in cold-region pavements due to its high permeability, low unit weight, and thermal insulating properties. On retaining walls and bridge abutments, TDA reduces earth pressure while providing drainage and thermal insulation. For vibration-mitigation applications, rubber-based aggregate systems have demonstrated promising damping and isolation capacity at a fraction of the cost.
Dr. El Naggar is also clear about where research gaps remain. More data is needed on long-term performance under cyclic loading. Better characterization of TDA with varying steel wire content would help engineers design with greater precision. The field is advancing because researchers like Dr. El Naggar and practitioners in the field keep closing the gap between what the lab shows and what the job site demands. That’s how progress happens. Not in one breakthrough moment, but in years of steady work connecting science to practice, research to results, potential to performance.
Fast Facts
- 1st USTMA State of Knowledge Report on TDA authored by Dr. El Naggar
- 25+ years of active TDA research in North America
- ASTM D6270-25: the standard engineers rely on to specify TDA
The USTMA State of Knowledge Report on Tire Derived Aggregate – authored by Dr. El Naggar – is available through the Tire Recycling Foundation at tirerecyclingfoundation.org.